The present invention relates generally to a method for the manufacture of welded pipes and, more particularly, to a method for preventing buckling or waving of edges of the strip in the manufacture of thin-walled welded tubular products.
Various types and kinds of pipes are used for various purposes. Among such pipes welded pipes are widely used because they can be fabricated in a relatively simple manner at low cost.
In the production of a welded pipe, the strip which is wound in the form of a coil is unwound and fed in an unheated condition through shaping rolls which gradually bring together the two longitudinal edges of the strip to bend the same into a tubular form circular in cross section, and finally the longitudinal edges of the strip are welded together. When the unheated strip is being bent, the longitudinal edges of the strip are subjected to tensile stress in the longitudinal direction and plastically deformed. However, when the edges are abutted against each other, the strip except its edge portions is subjected to tensile stress while the edge portions are subjected to compressive stress due to the plastic strain at the edge portion during the bending process. As a result, during the welding process, the edges are subject to buckling or waving along the weld line. In the case of thick-walled pipes, such buckling or edge waving hardly occurs, but in the case of thin-walled pipes, it frequently occurs. Therefore, it has been difficult to manufacture thin-walled welded pipes.